1. Technical Field
Aspects of the present disclosure relate in general to electronic circuitry. In particular, aspects of the disclosure include an electro-static discharge (ESD) clamp designed to be used with a high-power VDD rail in a single gate complementary metal oxide semiconductor (CMOS) circuit.
2. Description of the Related Art
Connections to integrated circuit (IC) inputs, outputs, and power are susceptible to electro-static discharge events that can damage internal components. An ESD event is a short discharge of electric energy caused by the sudden release of an electro-static build-up of electrical charge. If electro-static discharge-induced currents flow suddenly and strongly through electronic components, the high currents can literally melt the carefully formed layers of an integrated circuit. A chip is particularly susceptible to electro-static discharge when it is not mounted into a larger circuit (e.g., mounted onto a printed circuit board). Electro-static discharge protection is therefore particularly important in maintaining the reliability of semiconductor products, and commercial integrated circuits are generally expected to sustain without damage an electro-static discharge event in excess of 2,000 volts, which is often denoted as the human-body-model ESD voltage.
Semiconductor devices are becoming increasingly complex, and at the same time the devices' circuitry is becoming smaller and more crowded on the devices to accommodate the new and complex functions. The decreased size and spacing of the Reliability in semiconductor circuits is an important aspect of chip design. With the increasing complexity of CMOS circuits and the increased density of the silicon on which the circuits reside, the power-supply voltage for such circuits are reduced for low-power applications. At the same time, the thickness of gate oxide is often scaled down to increase circuit operating speed. However, this scaling increases the number of semiconductor processing steps.
Another issue with thinner gate-oxides is that the gate-oxide may become overstressed.
In a conventional power supply clamp circuit 1000 is shown in FIG. 1. The circuit 1000 may include a high-performance IC 110 or high-voltage circuit 120, and an active ESD clamp 100. ESD clamp 100 works during ESD events to provide a current path from the input pad 130A-B or power supply VDD to the substrate bias voltage supply, VSS, which is normally ground, or to another circuit element that is equipped to absorb the ESD current. In a conventional power supply clamp circuit, the power supply line is routed to ground through a clamp transistors that is biased to be “off” during normal circuit operation. When a voltage in excess of the maximum allowed voltage on a power supply line is detected by the ESD protection circuit, the clamp transistor will turn “on,” thereby shunting the induced ESD potential to ground.